(i). This reaction is an exothermic reaction. Sodium hydroxide being a strong base, completely dissociated in aqueous medium. The heat evolved increases the stability. This phenomenon is strong enough to prove that sodium hydroxide crystals are readily dissolved in water.
(ii). NaCl is geologically stable. If kept dry, it will remain a free flowing solid for years. Water can dissolve NaCl because the Na+ ions are attracted by OH- in water and Cl- ions are attracted by H+ in water. The solubility of NaCl does not increase the temperature. Based on this, NaOH is much more soluble due to exothermic nature than sodium chloride.
